1. Field of the Invention
The present invention generally relates to an ignition flux and a welding method and, more particularly, to an ignition flux for arc stud welding and an arc stud welding method.
2. Description of the Related Art
According to a conventional arc stud welding (or drawn arc stud welding) method, a welding portion of a fastener is positioned into contact with a welding zone of a metal workpiece. When an electric current flows through the fastener to the metal workpiece, and then the fastener is lifted from the metal workpiece, thus drawing an electric arc between the fastener and the metal workpiece. Consequently, the welding portion of the fastener and the welding zone of the metal workpiece are melted by the heat of said electric arc. Finally, a mechanical force is applied to the fastener, plunging the welding portion of the fastener into the welding zone of the metal workpiece, resulting in a welded joint. For instance, the fastener can be a screw bolt or a stud, and the metal workpiece can be a metal sheet or a metal tube.
In practice, the above described process is usually carried out with an arc stud welding machine. The arc stud welding machine includes a welding gun for holding the fastener. When such a machine is switched on, a voltage is applied to the fastener to form a current flowing from the fastener to the metal workpiece, such that the electric current flows through the fastener to the metal workpiece. A push-pull mechanism will then lifts off the fastener from the metal workpiece to draw an electric arc, consequently melting the welding portion of the fastener and the welding zone of the metal workpiece. After a predetermined arcing time, the push-pull mechanism will applied the mechanical force to plunge the fastener into a molten pool formed on the metal workpiece, forming a soundness joint connecting the fastener and the metal workpiece after the molten pool cools down. The arc stud welding process has high efficiency, and is widely used for shipbuilding, building, bridge constructions, automotive bodies, mechanical equipments, chemical equipments, and electricity equipments.
Particularly, when a fastener with a large diameter is used, it is usually required to dig a small hole at the center of its welding portion and to insert an ignition tip into said hole before drawing the electric arc for welding. Without the ignition tip, the electric arc cannot be easily created and smoothly formed, thus the fastener and the metal workpiece cannot sufficiently melt to tightly connect with each other. However, the insertion process of the ignition tip is complicated with high cost, significantly reducing welding efficiency and increasing the cost of production.